JPH1117642A - Receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain stable reception characteristics at all times, even in the case that a propagation environment has changed extensively by measuring the delay time of delay waves generated by multipath and changing the band width of a band width variable filter which corresponds to the measured delay time. SOLUTION: In a time response measurement part 7, from the time response of a transmission line, the delay time of the delay waves by the multipath is measured. A band width setting part 8 sets the band width of a band width variable filter 9 to an appropriate value, by using the delay time output of the time response measurement part 7. Then, the delay time of the delay waves generated by the multipath is measured, and the band width of the band width variable filter 9 is changed corresponding to the measured delay time. Thus, even in the case that the propagation environment is has changed extensively in the band width variable filter 9, a transmission line response inputted from a transmission line response calculation part 5 can be filtered in an appropriate band at all times and the stable reception characteristics are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving apparatus used in a wireless communication system employing an orthogonal frequency division multiplexing (hereinafter, referred to as OFDM).

[0002]

2. Description of the Related Art In recent years, there has been a demand for wireless transmission of large-capacity information such as data, image signals, and digital broadcasts.
For that purpose, it is essential to use a high-efficiency modulation method such as 16-level QAM or 64QAM. 16-value QAM and
64QAM or the like is a modulation method in which information is carried on each of an amplitude and a phase, and a signal modulated by this modulation method is demodulated into an original data sequence by synchronous detection.

[0003] In a general wireless communication system, the amplitude and phase of a signal waveform are greatly distorted due to a poor propagation environment such as multipath.

When a radio wave having such a signal waveform is received by a receiving apparatus and synchronous detection is performed using the received signal as it is, a result of obtaining a received data sequence completely different from the original data sequence results.

Therefore, in order to perform synchronous detection from radio waves affected by multipath or the like, it is necessary to provide a distortion compensating means for compensating for distortion such as amplitude distortion and phase distortion in the receiving apparatus.

Here, a conventional receiving apparatus provided with a distortion compensating means in a radio communication system employing an orthogonal frequency division multiplexing system (hereinafter referred to as an OFDM system) which is one of the multicarrier transmission systems will be described.

In the case of the OFDM system, the frequency characteristics of a transmission path can be obtained by using an orthogonal frequency division multiplex signal, that is, a plurality of subcarrier signals adjacent to the OFDM signal. Therefore, in a conventional wireless communication system, a transmitting apparatus periodically transmits a subcarrier signal on which a known signal is added, and when the receiving apparatus receives the subcarrier signal, a transmission path response of each subcarrier is obtained. OFDM
The transmission path response within the band of the signal is required. Since the transmission path response of each of these subcarriers includes thermal noise generated in the receiving device, the obtained transmission path response is filtered on the frequency axis to suppress noise components and improve the transmission path response. By approaching the true value, the distortion compensating means performs distortion compensation of the received signal using a transmission path response close to the true value after filtering, and demodulates the received signal to obtain a demodulated signal having good frequency characteristics.

By the way, the receiving device of this type of wireless communication system is sometimes used as a portable mobile terminal in recent years, and its position is not always fixed, and receives a radio wave while moving. Sometimes. In this mobile reception, since the propagation environment changes drastically, the transmission path response also changes greatly.

Conventionally, several filters having different bandwidths are provided in the receiving apparatus, and a known signal having a strong correlation in the time axis direction is periodically transmitted on the transmitting side, and the known signal is transmitted to the receiving apparatus. Filtering the transmission path response by selectively using an appropriate filter upon reception is performed. If the bandwidth of the selected filter is wider than the appropriate value, the transmission path response after filtering contains much noise, and if the bandwidth is narrow, the frequency characteristics of the transmission path may be distorted, and in both cases excellent reception characteristics are obtained. Therefore, it is desirable to select and use a filter having an appropriate bandwidth. However, when performing mobile reception, since the propagation environment changes drastically every moment, even if an appropriate filter is selected once, the filter to be used must be selected again due to a subsequent change in the state of the transmission path. Further, in using the receiving device as a mobile terminal, there is no way to provide many filters having different bandwidths in the device from the viewpoint of securing portability, and there is a limit to the selective use. Further, since the known signal is transmitted every few symbols even though it is periodically, if the propagation environment changes greatly during these several symbols, the band of the filter used may be largely deviated from an appropriate value. is there.

[0010]

As described above, in the above-mentioned conventional receiving apparatus, several filters having different bandwidths are provided, and an appropriate filter is selectively used according to the propagation environment. In the case of reception, since the propagation environment changes drastically every moment, there is a limit in selecting and using a filter, and there has been a problem that stable reception characteristics cannot be obtained. SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and a first object of the present invention is to provide a receiving apparatus capable of always obtaining stable receiving characteristics even when the propagation environment changes greatly. .

A second object of the present invention is to provide a receiving apparatus capable of filtering a transmission path response with an optimum bandwidth even if a known signal transmission interval is provided.

[0012]

According to a first aspect of the present invention, there is provided a receiving apparatus for receiving an orthogonal frequency division multiplexed signal, and a receiving apparatus for receiving the orthogonal frequency division multiplexed signal. First conversion means for converting a received signal into a frequency spectrum, reference frequency spectrum signal generating means for generating a reference frequency spectrum signal for reference to the received signal, and reception frequency spectrum converted by the first conversion means A channel response calculating unit for calculating a channel response from the signal and the reference frequency spectrum signal generated by the reference frequency spectrum signal generating unit; and a transmission line response calculated by the channel response calculating unit. Second conversion means for converting the response to a response, and multipath using the time response of the transmission path converted by the second conversion means. Delay time measuring means for measuring the delay time of the delayed wave, and the bandwidth for filtering the transmission path response can be set variably, and the transmission path response calculated by the transmission path response calculation means is set. A variable bandwidth filter that filters by a bandwidth, a bandwidth setting unit that sets a bandwidth of the variable bandwidth filter according to a delay time of the delayed wave measured by the delay time measuring unit, and the variable bandwidth filter And a distortion compensator for compensating for a distortion in the frequency axis direction due to multipath of the reception frequency spectrum signal converted by the first converter using the transmission path response filtered by the first converter. Demodulation means for demodulating a digital data sequence using the reception frequency spectrum signal.

According to the first aspect of the present invention, the delay time of the delay wave generated in the multipath is measured, and the bandwidth of the bandwidth variable filter is changed according to the measured delay time. Even if it changes, the transmission path response calculated by the transmission path response calculation means can always be filtered with an appropriate bandwidth, and stable reception characteristics can be obtained.

According to a second aspect of the present invention, there is provided a receiving apparatus for receiving an orthogonal frequency division multiplexed signal, a reference frequency spectrum signal generating means for generating a reference frequency spectrum signal for reference to the received signal, A transmission line response calculation unit that calculates a transmission line response from a reference frequency spectrum signal generated by the reference frequency spectrum signal generation unit and a frequency spectrum signal obtained by converting the reception signal; Conversion means for converting the received signal into a frequency spectrum and converting the transmission path response calculated by the transmission path response calculation means into a time response of the transmission path, and a signal switching means for switching input / output of a signal to the conversion means And the time response of the transmission path converted by the conversion means and output from the signal switching means. A delay time measuring means for measuring a delay time of a delay wave due to multipath; a bandwidth for filtering the transmission path response can be set variably; and a transmission path response calculated by the transmission path response calculation means is set. A variable bandwidth filter for filtering with the set bandwidth, a bandwidth setting means for setting a bandwidth of the variable bandwidth filter according to a delay time of the delay wave measured by the delay time measuring means, and the bandwidth Distortion compensating means for compensating for distortion in the frequency axis direction due to multipath of a received frequency spectrum signal converted by the converting means and output from the signal switching means, using a transmission path response filtered by a variable filter; Demodulating a digital data sequence using a reception frequency spectrum signal distortion-compensated by means It is and a stage.

In the case of the present invention, the converting means converts the received signal received by the receiving means into a frequency spectrum and converts the transmission path response calculated by the transmission path response calculating means into the time of the transmission path. To a response,
By switching the input / output signal to the conversion means by the signal switching means, it is possible to operate in the same manner as in the first aspect of the present invention.

That is, the first conversion means and the second conversion means are integrated, and a signal switching means for switching input / output signals to the conversion means is provided. It operates in the same manner as the present invention, and can have a simpler configuration than the receiving apparatus of the first aspect of the present invention.

According to a third aspect of the present invention, in the receiving apparatus according to the first aspect, a modulating means for remodulating a demodulated signal demodulated by the demodulating means and outputting a remodulated signal; Signal switching means for switching between the re-modulated signal output from the controller and the reference frequency spectrum signal generated by the reference frequency spectrum signal generation means and outputting the signal to the transmission path response calculation means; and Delay means for delaying the reception frequency spectrum signal to the road response calculation means.

In the third aspect of the invention, when a known signal is first received as a reception signal, the signal switching means outputs the reference frequency spectrum signal to the transmission path response calculation means and performs signal processing in the same manner as in the above invention. And demodulated by demodulation means. The demodulation signal demodulated by the demodulation means is modulated again by the modulation means and outputs a remodulated signal to the signal switching means, which in turn outputs the remodulated signal to the transmission line response calculation means. Then, the re-modulated signal and the delayed reception frequency spectrum signal from the first converter are input to the transmission path response calculation means, and the transmission path response is calculated.

By this means, if a known symbol having a strong correlation in the time axis direction, which has been conventionally transmitted for synchronization acquisition and the like, is received by the receiving device only once at the beginning, then the feedback from the demodulated signal immediately follows. The transmission path response can be calculated from the obtained data, and thereafter, not only the calculation of the correlation value is unnecessary, but also the transmission of the known symbol from the transmission side becomes unnecessary. If necessary, if known symbols are transmitted at a wider interval than in the related art, it is possible to correct a deviation in accuracy due to a demodulation error. As a result, the transmission path response can be filtered with the optimum bandwidth even if the transmission interval of the known signal is increased.

According to a fourth aspect of the present invention, there is provided a receiving apparatus for receiving an orthogonal frequency division multiplexed signal, a first converting means for converting a received signal received by the receiving means into a frequency spectrum, A reference frequency spectrum signal generating means for generating a reference frequency spectrum signal for reference to the received signal; a received frequency spectrum signal converted by the first converting means; and a reference frequency generated by the reference frequency spectrum signal generating means. Transmission path response calculation means for calculating a transmission path response from the spectrum signal; second conversion means for converting the transmission path response calculated by the transmission path response calculation means into a time response of the transmission path; Using the time response of the transmission path converted by the conversion means, the arrival time of the desired wave and the arrival of the Obtains a reception power of time and each of the received signals, and a reception signal processing means for performing reception signal processing using them.

In the case of the present invention, the transmission line response calculated by the transmission line response calculating means is converted into a time response, and the delay time of each delay wave is measured using the time response. The received signal processing according to the measurement result is performed by the received signal processing means. That is, claim 1
The measurement results of the delay time can be used for applications other than the inventions described in (1) to (3).

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an OFDΜ receiving apparatus according to a first embodiment of the receiving apparatus of the present invention.
This OFDΜ receiving apparatus is a synchronous detection OFDM receiving apparatus that filters a transmission path response calculated from a reception reference symbol and a transmission reference symbol in the frequency axis direction and compensates for distortion of a reception symbol with the filtered transmission path response.

As shown in FIG. 1, the OFDΜ receiving apparatus includes a receiving section 2 for receiving an orthogonal frequency division multiplexed signal (OFDΜ symbol) via an antenna 1, and a receiving section 2.
A fast Fourier transform unit (FFT) 4 as a first transform unit for transforming a received signal received by the above into a frequency spectrum (such as a data symbol or a known reference symbol);
When the received signal is a reference symbol (known signal), a reference frequency spectrum signal for the reference symbol, that is, a transmission reference symbol generation unit 3 as reference frequency spectrum signal generation means for generating a transmission reference symbol, and a fast Fourier transform unit (FFT) 4, a transmission path response calculation section 5 that calculates a transmission path response from the transmission reference symbol output from the transmission reference symbol generation section 3, and the transmission path response calculation section 5. High-speed inverse Fourier transform unit as second conversion means for converting the obtained transmission path response into a time response of the transmission path (such as the arrival time of a desired wave and the arrival time of a delayed wave received after being delayed from the desired wave) (IFFT) 6 and the time response of the transmission path converted by the fast inverse Fourier transform unit (IFFT) 6 using multipath. The delay time measuring unit 7 for measuring the delay time of the delay wave and the bandwidth for filtering the transmission line response can be set variably, and the transmission line response calculated by the transmission line response calculation unit 5 is set. And a bandwidth setting unit 8 for setting the bandwidth of the bandwidth variable filter 9 according to the delay time of the delay wave measured by the delay time measuring unit 7.
And a fast Fourier transform unit (FFT) 4 using the transmission path response filtered by the bandwidth variable filter 9.
From a distortion compensator 10 for compensating for distortion in the frequency axis direction due to multipath of a received signal converted by the above, and a demodulator 11 for demodulating a digital data sequence using the received signal distortion-compensated by the distortion compensator 10. It is configured.

In the case of the OFDΜ receiving apparatus according to the first embodiment, the OFDM symbol received by the antenna 1 is subjected to reception signal processing by the receiving unit 2, and is subjected to fast Fourier transform (FFT) by the fast Fourier transform unit 4. It is converted to a frequency spectrum signal.

Here, when a known reference symbol transmitted from the transmitting side at a predetermined period is received, the transmission path response calculation section 5 generates a frequency spectrum signal of the reception reference symbol and the transmission reference symbol generation section 3 A transmission path response is calculated using the frequency spectrum signal of the transmission reference symbol thus calculated, and the calculated transmission path response is converted to a fast inverse Fourier transform unit (I
FFT) 6.

When the transmission path response is input to the fast inverse Fourier transform unit (IFFT) 6, the fast inverse Fourier transform unit (IFFT) 6
In FT) 6, the transmission path response is subjected to fast inverse Fourier transform to obtain a time response of the transmission path, which is output to the time response measuring unit 7.

The time response measuring section 7 measures the delay time of the delay wave due to multipath from the time response of the transmission path.
The bandwidth setting unit 8 uses the delay time output of the time response measurement unit 7 to set the bandwidth of the bandwidth variable filter 9 to an appropriate value.

Since the transmission path response calculated by the transmission path response calculation section 5 includes a noise component, the transmission path response is output from the transmission path response calculation section 5 to the bandwidth variable filter 9. When the transmission path response is input to the bandwidth variable filter 9, the transmission path response is filtered in the frequency axis direction with the bandwidth set by the bandwidth setting unit 8, and the noise component included in the transmission path response is reduced. Is suppressed.

On the other hand, when the receiving section 2 receives a data symbol instead of a reference symbol, the fast Fourier transform section 4 converts the data symbol into a frequency spectrum, and the distortion compensating section 10 performs filtering performed by the filter 8. Using the subsequent transmission path response and the frequency spectrum signal of the data symbol output from the fast Fourier transform unit 4, the distortion of the received data symbol in the frequency axis direction is compensated. The data symbol on which the distortion compensation has been performed by the distortion compensator 10 is demodulated by the demodulator 11 into a digital data sequence.

As described above, according to the OFDM receiver of the first embodiment, the delay time of the delay wave generated by the multipath is measured, and the bandwidth of the bandwidth variable filter 9 is determined in accordance with the measured delay time. Therefore, even if the propagation environment changes greatly, the bandwidth variable filter 9 can always filter the transmission path response input from the transmission path response calculation unit 5 with an appropriate bandwidth, and achieve stable reception characteristics. Can be obtained. In addition, since the delay time is measured from the transmission path response in which noise is suppressed, the accuracy of measuring the delay time can be improved. Next, a receiving apparatus according to a second embodiment of the present invention will be described with reference to FIG. FIG. 2 is a block diagram showing an example of an OFDM receiver in which the fast Fourier transform unit 4 and the fast inverse Fourier transform unit 6 of FIG. 1 are integrated into a fast Fourier / inverse Fourier transform unit 13.

In general, the fast Fourier transform (FFT) and the inverse Fourier transform (IFFT) have almost the same processing form, that is, the algorithms are almost the same, so that the fast Fourier transform unit 4 and the fast inverse Fourier transform unit 6 shown in the first embodiment are different from each other. Can be realized as the same circuit configuration. Therefore, the OFDM receiving apparatus according to the second embodiment includes a switching unit 12- at the input terminal and the output terminal of the fast Fourier / inverse Fourier transform unit 13, respectively.
1 and 12-2, and when the signal output from the receiving unit 2 is input to the fast Fourier / inverse Fourier transform unit 13 via the switching unit 12-1, the fast Fourier / inverse Fourier transform unit 13 FFT is performed, and the result of this conversion is
-2 is switched to the transmission path response calculation unit 5 or the distortion compensation unit 10, and the signal output from the transmission path response calculation unit 5 is converted to the fast Fourier / inverse Fourier transform unit 1 via the switching unit 12-1.
3, the fast Fourier / inverse Fourier transform unit 13 performs an IFFT, and outputs the transform result to the switching unit 12-2.
Is output to the time response measurement unit 7.

In the case of the OFDM receiving apparatus according to the second embodiment, the OFDM symbol received by the antenna 1 is subjected to received signal processing by the receiving unit 2, passed through the switching unit 12-1, and passed through the fast Fourier / inverse Fourier. It is input to the converter 13. The fast Fourier / inverse Fourier transform unit 13 converts a received symbol into a frequency spectrum signal by fast Fourier transform.

Here, when the received symbol is, for example, a known reference symbol, the output of the fast Fourier / inverse Fourier transform unit 13 is input to the transmission path response calculation unit 5 through the switching unit 12-2. The transmission path response calculation unit 5 uses the frequency spectrum of the received known reference symbol obtained from the switching unit 12-2 and the frequency spectrum of the transmission known reference symbol generated by the transmission reference symbol generation unit 3 to transmit the transmission path. Calculate the response. The calculated transmission path response is filtered by the variable bandwidth filter 9 to suppress noise. The output of the transmission path response calculation unit 5 is input to the fast Fourier / inverse Fourier transform unit 13 via the switching unit 12-1.

Then, the fast Fourier / inverse Fourier transform unit 13 performs an inverse Fourier transform on the input transmission path response and converts it into a time response of the transmission path. The converted time response of the transmission path is input to the time response measuring unit 7 via the switching unit 12-2, and the time response measuring unit 7 measures the delay time of the delayed wave, and sets the delay time to the bandwidth setting. Output to the unit 8.

The bandwidth setting unit 8 sets an appropriate bandwidth of the bandwidth variable filter 9 according to the delay time input from the time response measurement unit 7.

On the other hand, when the data symbol is received by the receiving unit 2, the output of the receiving unit 2 is input to the fast Fourier / inverse Fourier transform unit 13 via the switching unit 12-1.
The fast Fourier / inverse Fourier transform unit 13 performs fast Fourier transform. The frequency spectrum of the data symbol obtained by the fast Fourier transform is input to the distortion compensation unit 10 via the switching unit 12-2. Distortion compensator 10
Then, the distortion in the frequency axis direction of the data symbol output from the switching unit 12-2 is compensated for using the transmission path response after filtering output from the bandwidth variable filter 9. The frequency spectrum of the data symbol after distortion compensation is demodulated by the demodulation unit 11 and converted into a digital data sequence.

As described above, according to the OFDM receiver of the second embodiment, the fast Fourier / inverse Fourier transform unit 13
Converts the received signal received by the receiving unit 2 into a frequency spectrum, and also converts the channel response calculated by the channel response calculating unit 5 into a time response of the channel.
The switching unit 12-1 disposed in the preceding stage and the switching unit 12-2 disposed in the subsequent stage switch input / output signals to the fast Fourier / inverse Fourier transform unit 13 to operate in the same manner as in the first embodiment. be able to.

That is, in the first embodiment, the fast Fourier transform unit (FFT) 4 and the fast inverse Fourier transform unit (I
And FFT) 6 are separated, but by integrating them, the same effects as in the first embodiment can be obtained, and the configuration inside the device is simplified as compared with the first embodiment. can do.

Since FFT and IFFT are processes for converting data by almost the same algorithm, the capacity of a single fast Fourier transform unit (FFT) 4 is set to 1, and the capacity of a single fast inverse Fourier transform unit (IFFT) 6 is set to 1. By combining the two components with each other and having the capacity of 2 as the fast Fourier / inverse Fourier transform unit 13, it is possible to package with a capacity of about 1 times that of a single unit.

Next, an OFD receiving apparatus according to a third embodiment of the present invention will be described with reference to FIG. FIG. 3 is a block diagram showing the configuration of the OFD receiver according to the third embodiment.

As shown in FIG.
The FDΜ receiving apparatus further includes, in addition to the configuration of the first embodiment, a modulating unit 15 that remodulates and feeds back the data sequence demodulated by the demodulating unit 11, a modulated signal fed back from the modulating unit 15, and a transmission reference symbol generation unit. A switching unit 12-3 for switching the transmission reference symbol generated in Step 3 and outputting the transmission reference symbol to the transmission path response calculation unit 5, and a switching unit 12-3
And a delay unit 14 for inputting the output of the fast Fourier transform unit 4 delayed when the signal output from is a re-modulated signal to the transmission line response calculation unit 5.

In the case of the OFDΜ receiving apparatus according to the third embodiment, the OFDM symbol received by the antenna 1 is subjected to reception signal processing by the receiving unit 2 and is subjected to fast Fourier transform (FFT) by the fast Fourier transform unit 4. Thereby, it is converted into a frequency spectrum signal. The output of the fast Fourier transform unit 4 is delayed by one symbol in the delay unit 14 and input to the transmission path response calculation unit 5.

For example, if the received OFDM symbol is a known reference symbol, the transmission reference symbol generation unit 3
Generates and outputs a frequency spectrum signal of a transmission reference symbol. The channel response calculation unit 5 calculates the channel response using the frequency spectrum signal of the received reference symbol and the frequency spectrum signal of the transmission reference symbol input to the channel response calculation unit 5 through the switching unit 12-3. calculate. Since the calculated transmission path response includes a noise component, the transmission path response is filtered by the bandwidth variable filter 9 in the frequency axis direction. The filtered transmission path response is subjected to an inverse Fourier transform by an inverse Fourier transform unit 6 to be converted into a time response.

Since the transmission path response after being filtered by the bandwidth variable filter 9 has suppressed noise components, it is better to measure the delay time using the IFFT result of the transmission path response after filtering. The measurement accuracy of the delay time is improved as compared with the case where the IFFT result of the road response is used.

The time response measuring section 7 measures the delay time of a multipath delayed wave from the time response of the transmission path.
The bandwidth setting unit 8 sets the bandwidth of the bandwidth variable filter 9 to an appropriate value using the measured delay time. This bandwidth may be used for filtering the channel response calculated from the received symbol at the current time, or may be used for filtering the channel response calculated from the next symbol. In this case, when filtering the transmission path response of the first symbol, the bandwidth of the bandwidth variable filter 9 has not been set to an appropriate value yet, so that it is set to a predetermined value in advance. The bandwidth of the bandwidth variable filter 9 for filtering the transmission path response of the leading symbol may be set from, for example, an expected maximum delay time, or may be set slightly larger. Also, the transmission path response of the first symbol need not be filtered.

In the third embodiment, the case has been described where the output of the bandwidth variable filter 9 is subjected to fast inverse Fourier transform (IFFT). However, as in the OFDM receiver of FIG. 1 or FIG. The output of the unit 5 may be subjected to a fast inverse Fourier transform (IFFT).

On the other hand, OFD received by the receiving unit 2
If the M symbols are data symbols, the fast Fourier transform unit 4 converts the data symbols into a frequency spectrum signal, and the distortion compensating unit 10 outputs the filtered transmission path response output from the bandwidth variable filter 9 and the fast Fourier transform. The distortion in the frequency axis direction of the received data symbol is compensated for using the frequency spectrum signal of the data symbol output from the conversion unit 4. The data symbol whose distortion has been compensated by the distortion compensating unit 10 is demodulated into a digital data sequence by the demodulating unit 11. The digital data sequence obtained by the demodulation unit 11 is re-modulated by the modulation unit 15 and input to the transmission path response calculation unit 5 via the switching unit 12-3. The received data symbols IFFTed by the fast Fourier transform unit 4 are delayed by one symbol by the delay unit 14 and then transmitted by the transmission line response calculation unit 5.
Is input to The transmission path response calculation unit 5 includes a switching unit 12-3.
And the output of the delay unit 14 are used to calculate the channel response again. The calculated transmission path response is filtered by the bandwidth variable filter 9 set to an appropriate value, and used for distortion compensation of the next symbol. When a data symbol is received in this way, distortion can be compensated for using the channel response obtained from the symbol one time earlier.
It is also possible to compensate for distortion using the transmission path response obtained from the symbol at the current time, but in this case, the time required to demodulate the received signal into a digital data sequence becomes longer.

The output of the bandwidth variable filter 9 is subjected to IFFT in the inverse Fourier transform unit 6, the delay time of the delay wave is measured in the time response measuring unit 7, and the measured delay time is measured as a bandwidth setting unit. 8 is output. When the measurement result is input from the time response measurement unit 7, the bandwidth setting unit 8
Bandwidth variable filter 9 according to the input delay time value
Reconfigure the bandwidth of. Thus, the bandwidth of the bandwidth variable filter 9 is updated (reset) every time the delay time is measured.

As described above, according to the OFDM receiver of the third embodiment, of the received OFDM symbols,
Not only when a known reference symbol is received but also when a data symbol is received, the bandwidth of the bandwidth variable filter 9 is reset according to the delay time of the delay wave, so that there is a time variation in the transmission path response. Even in such a case, the bandwidth of the bandwidth variable filter 9 can always be set to an appropriate value. In other words, even when the propagation environment changes greatly while the known signal is not received from the transmitting side, the delay time of the delay wave can be continuously measured by the data obtained immediately before, and the bandwidth of the bandwidth tunable filter 9 can always be measured. It can be set to an appropriate value.

FIG. 4 shows F calculated by computer simulation.
FIG. 9 is a diagram illustrating a channel response to an OFDM symbol having an FT scale of 256 and a symbol length of 1 [msec]. Transmission line is Eb / N
This is a three-wave model of o = 10 [dB], the delay times of the delayed waves are 10 [μsec] and 50 [μsec], respectively, and the D / U is 0 [dΒ] and 5 [dΒ], respectively.

From FIG. 4, it can be seen that fine irregularities are seen in the output of the transmission path response calculator 5 because noise is added. The transmission path response obtained by filtering the output of the transmission path response calculation unit 5 has the noise component suppressed and approaches the true value of the transmission path response. The subcarrier interval of OFDM is W [Hz], and the one-sided bandwidth in the time domain of the filter is B [1 / Hz]. If the normalized bandwidth in the time domain of the filter is defined as a one-sided bandwidth in the time domain for the symbol length 1 / W, the normalized bandwidth is represented by BW. In FIG. 4, ΒW = 0.08,
A low-pass roll-off filter with a tap length of 64 is used. For setting the bandwidth, the IFFT result of the transmission path response is used.

FIG. 5 is a diagram showing the time response of the transmission path obtained by IFFT of the output of the transmission path response calculation section 5 in FIG. 4 by the fast inverse Fourier transform section 6 having a scale of 256.

As shown in the figure, the symbol length is 1 [msec].
Since the signal of (subcarrier interval 1 [KHz]) is IFFT, the sampling interval of the signal after IFFT is 1/2.
56 [msec].

The received power spectrum shown in FIG.
There are peaks at the 131st, 141st, and 141st sampling times, respectively. The peak at the 129th sampling time is due to the desired signal, and the peak at the 131st, 141st sampling time is due to the delayed wave.
2 samples between the 131st peak and the peak of the desired wave,
There is a time interval of 12 samples between the 141st peak and the peak of the desired wave, which is about 7.8 [μsec
], 46.9 [μsec]. Since the actual delay times are 10 [μsec] and 50 [μsec], respectively, they almost coincide with the peak interval times, and it can be confirmed that the delay time of the delay wave can be measured by the IFFT of the transmission path response.
Here, the sampling interval is 1/256 [msec], but if the sampling interval is reduced, the accuracy of the delay time measurement is improved. Also, by reading the peak value, the power value of the arriving received signal can be determined. Since a high-power delayed wave greatly affects the formation of a transmission path response, it is preferable to determine the filter bandwidth by measuring the delay time of the high-power delayed wave.

FIG. 6 is a diagram showing the bit error rate characteristics of the receiving apparatus of FIG. 1 when the horizontal axis is the normalized bandwidth ΒW.

The transmission path has a delay time of 10 [μsec], D / U
= 0 [dΒ] first two-wave model, delay time 50 [μsec]
], The second two-wave model of D / U = 5 [dB], the delay times of the two delayed waves are 10 [μsec] and 50 [μsec], respectively.
] And D / U are three types of three-wave models of 0 [dB] and 5 [dB], respectively, and Eb / No = 10 [d] respectively.
B]. The bandwidth variable filter 9 uses a 64-tap roll-off filter. According to FIG. 6, the optimum bit error rate in the three-wave model is the bandwidth ΔW = 0.07, which is almost equal to the optimum bandwidth 0.08 in the second two-wave model. In this case, it is understood that the bandwidth should be set from the maximum delay time. However, since a delay wave with low reception power has almost no effect on the formation of the transmission path, it is preferable to measure the maximum delay time from the delay waves with high reception power and set the bandwidth from the measured maximum delay time.

Next, a receiving apparatus according to a fourth embodiment of the present invention will be described with reference to FIG. FIG. 7 is a block diagram illustrating a configuration of an OFDM receiver according to a fourth embodiment of the present invention.

The OFDM receiver according to the fourth embodiment has
Received signal measurement for measuring a received signal in order to use the arrival times of the desired wave and the delayed wave obtained by IFFT of the transmission path response and the respective received powers for the received signal processing such as synchronization acquisition performed in the receiver 2. A section 70 is provided.

In the case of the OFDM receiver of the fourth embodiment, the OFDM symbol received by the antenna 1 is subjected to reception signal processing by the receiver 2 and FFT performed by the fast Fourier transformer 4 to obtain a frequency spectrum. Converted to a signal. When a known reference symbol is received, the channel response calculation unit 5 calculates a channel response using the frequency spectrum signal of the reception reference symbol and the frequency spectrum signal of the transmission reference symbol generated by the transmission reference symbol generation unit 3. I do. Since the calculated transmission path response includes a noise component, the transmission path response is filtered by the bandwidth variable filter 9 in the frequency axis direction.

The transmission path response calculated by the transmission path response calculation section 5 is subjected to IFFT by a fast inverse Fourier transform section (IFFT) 6 to obtain the time response of the transmission path, that is, the arrival times of the desired wave and the delayed wave. .

From the times of the desired wave and the delayed wave, the received signal measuring unit 70 measures the delay time of the delayed wave and the respective received power values, and feeds back to the receiving unit 2. Receiver 2
Then, the reception signal processing such as synchronization supplementation is performed using the delay time of the delay wave and the reception power values of the desired wave and the delay wave input from the reception signal measurement unit 70.

As described above, according to the receiving apparatus of the fourth embodiment, the fast inverse Fourier transform (IFFT) 6
By measuring the delay time from the arrival of the desired wave to the arrival of the delayed wave from the time response of the transmission path obtained by T and the received power value of each of the desired wave and the delayed wave,
The measurement results can be used for applications different from those of the first to third embodiments, for example, for supplementing synchronization in the receiving unit 2.

[0064]

As described above, according to the first aspect of the present invention, the delay time of the delay wave generated in the multipath is measured, and the bandwidth of the variable bandwidth filter is determined according to the measured delay time. As a result, even if the propagation environment changes greatly, the transmission path response calculated by the transmission path response calculation means can always be filtered with an appropriate bandwidth, and stable reception characteristics can be obtained. In addition, since the delay time is measured from the transmission path response in which noise is suppressed, the accuracy of measuring the delay time can be improved.

According to the second aspect of the present invention, there is provided a converting means integrating the first converting means and the second converting means,
By providing the signal switching means for switching the input / output signal to the conversion means, the configuration of the receiving device can be simplified.

According to the third aspect of the present invention, even when the propagation environment greatly changes while the known signal is not transmitted on the transmitting side, the delay time of the delayed wave is continuously measured by the data obtained by the receiving apparatus itself. Can be. Therefore, conventionally,
It is only necessary to transmit a symbol having a strong correlation in the time axis direction, that is, a known signal, transmitted for synchronization acquisition or the like, at a wider interval than before or only once at the beginning. As a result, the transmission path response can be filtered with the optimum bandwidth even if the transmission interval of the known signal is increased. Claim 4
According to the invention described above, the measurement result of the delay time can be used for applications other than the inventions described in the first to third aspects.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an OFDM receiver according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an OFDM receiver according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of an OFD receiver according to a third embodiment of the present invention;

FIG. 4 is an exemplary view showing a transmission path response characteristic of the OFDM receiver according to the embodiment;

FIG. 5 is a diagram showing an inverse Fourier transform result of a transmission path response of the OFDM receiver according to the embodiment.

FIG. 6 is a diagram showing a bit error rate characteristic of the OFDM receiver according to the embodiment.

FIG. 7 is a block diagram showing a configuration of an OFD receiving apparatus according to a fourth embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reception antenna, 2 ... Reception part, 3 ... Transmission reference symbol generation part, 4 ... Fast Fourier transformation part, 5 ... Transmission path response calculation part, 6 ... Fast inverse Fourier transformation part, 7 ... Time response measurement part,
8: bandwidth setting unit, 9: filter, 10: distortion compensation unit,
11 demodulation unit, 12-1, 12-2, 12-3 switching unit, 13 modulation unit, 14 delay unit, 15 modulation unit.

Claims (4)

[Claims] A receiving unit that receives an orthogonal frequency division multiplexed signal; a first converting unit that converts a received signal received by the receiving unit into a frequency spectrum; and a reference frequency for reference to the received signal. A reference frequency spectrum signal generating means for generating a spectrum signal; and a transmission path response calculated from the received frequency spectrum signal converted by the first converting means and the reference frequency spectrum signal generated by the reference frequency spectrum signal generating means. Transmission line response calculation means, a transmission line response calculated by the transmission line response calculation means, a second conversion means for converting the transmission line response into a time response of the transmission line, and a transmission path converted by the second conversion means. Delay time measuring means for measuring a delay time of a multipath delayed wave using a time response; A variable bandwidth for filtering the transmission path response calculated by the transmission path response calculation means with the set bandwidth, and the delay time measurement means Bandwidth setting means for setting the bandwidth of the variable bandwidth filter according to the delay time of the delayed wave; and a transmission path response filtered by the variable bandwidth filter, wherein the transmission path response is converted by the first conversion means. Distortion compensation means for compensating for distortion in the frequency axis direction due to multipath of the reception frequency spectrum signal; and demodulation means for demodulating a digital data sequence using the reception frequency spectrum signal distortion-compensated by the distortion compensation means. A receiving device characterized by the above-mentioned. 2. A receiving means for receiving an orthogonal frequency division multiplexed signal; a reference frequency spectrum signal generating means for generating a reference frequency spectrum signal for reference to the received signal; Channel response calculating means for calculating a channel response from the obtained reference frequency spectrum signal and a frequency spectrum signal obtained by converting the received signal; and converting the received signal received by the receiving means into a received frequency spectrum. A conversion unit that converts the transmission line response calculated by the transmission line response calculation unit into a time response of a transmission line; a signal switching unit that switches input and output of a signal to and from the conversion unit; Delayed wave due to multipath using the time response of the transmission path output from the signal switching means A delay time measuring means for measuring a delay time, a bandwidth for filtering the transmission path response can be set variably, and a transmission path response calculated by the transmission path response calculation means is filtered with the set bandwidth. A variable bandwidth filter, a bandwidth setting unit that sets a bandwidth of the variable bandwidth filter according to a delay time of the delay wave measured by the delay time measuring unit, and a filter that is filtered by the variable bandwidth filter. Using a transmission path response, a distortion compensating means for compensating for distortion in the frequency axis direction due to multipath of the received frequency spectrum signal converted by the converting means and output from the signal switching means, and distortion compensated by the distortion compensating means Demodulating means for demodulating a digital data sequence using the reception frequency spectrum signal. Receiving device for the butterflies. 3. The receiving apparatus according to claim 1, wherein the demodulation signal demodulated by the demodulation means is re-modulated to output a re-modulated signal; A signal switching unit that switches the reference frequency spectrum signal generated by the reference frequency spectrum signal generation unit and outputs the signal to the transmission line response calculation unit; and a reception frequency spectrum from the first conversion unit to the transmission line response calculation unit. A receiving device comprising: delay means for delaying a signal. 4. A receiving means for receiving an orthogonal frequency division multiplexed signal; a first converting means for converting a received signal received by the receiving means into a frequency spectrum; and a reference frequency for reference to the received signal. A reference frequency spectrum signal generating means for generating a spectrum signal; and a transmission path response calculated from the received frequency spectrum signal converted by the first converting means and the reference frequency spectrum signal generated by the reference frequency spectrum signal generating means. Transmission line response calculation means, a transmission line response calculated by the transmission line response calculation means, a second conversion means for converting the transmission line response into a time response of the transmission line, and a transmission path converted by the second conversion means. Using the time response, the arrival time of the desired wave, the arrival time of the delayed wave due to multipath of the desired wave, and the Obtains a transmission power, the receiving apparatus characterized by comprising a reception signal processing means for performing reception signal processing using them.